The present invention relates to novel yeasts and the use thereof.
Bread is grouped in a wide variety of items, including French bread with no sugar added, white bread having a low sugar range, which is prepared by adding sugar in an amount of 5 to 6% to flour, croissants and butter rolls having a medium sugar range, which are prepared by adding sugar in an amount of 8 to 15% to flour, Danish pastry and confectionery bread having a high sugar range, which are prepared by adding sugar in an amount of 20 to 30% to flour, fermented confectioneries, such as beam-jam sweet, and coffee cake and brioche, which are prepared by adding sugar in an amount of 35 to 50% to flour. Furthermore, bakery processes can be divided into scratch process (including straight bakery process and intermediate seed bakery process) and frozen dough processes. Therefore, these processes and bread items are used in such a wide variety of combinations.
For producing the bread items in the low sugar range to the high sugar range, conventionally, various yeasts with various fermentative abilities have been used in such a complicated manner that yeast with high freezing tolerance should be used for the frozen dough process. However, no yeast with sugar tolerance enough for fermentation of dough items [for bean-jam sweet roll, fermented confectioneries, etc.] in a blend of sugar at a content as high as 35% or more to flour has yet been present. Accordingly, many bakers have managed to treat such dough items by prolonging the duration of the fermentation more than necessary or raising the quantity of yeast, to prepare the products. Nevertheless, these products are currently of no bread quality primarily intended and have poor bulky appearance.
It is an object of the invention to provide yeasts with high sugar tolerance (or osmotic pressure tolerance) having high excellent fermentative abilities in a super-high sugar range, so as to solve the problems. In current circumstances where sweet bread and confectioneries with high sugar contents are desired in general, more specifically, the invention has been attained for the purpose of providing novel yeasts with super-high.sugar tolerance, which conventionally have never existed and are hardly affected (of which the fermentative abilities are hardly reduced) by the osmotic pressure of high contents of fat or fatty oil or egg blended in dough at a super-high sugar content of 30 to 40% or more. Conventional yeasts under the influence of osmotic pressure can never yield bread products of excellent quality from dough in a blend of fat or fatty oil or egg at a super-high sugar content of 30 to 40% or more. Owing to the progress in bakery technology and the diversification of bread items in recent years, yeast should be selected and used, depending on the intended bread item. Thus, many types of yeast are essentially needed. In terms of laborious works in the use of a different yeast each time, which is not practical industrially, novel yeasts with excellent properties are provided, from the respect that one yeast concurrently having these properties can satisfy the whole aspect.
In other words, the invention provides excellent yeasts with great specificity from the respect of super-high sugar tolerance. Additionally, the invention can firstly provide new useful yeasts satisfying all the needs, which has never been obtained conventionally and which does not require the proper use of yeasts having different properties, depending on the intended products.
The invention relates to yeasts which high sugar tolerance (or osmotic pressure tolerance). Specific characteristic properties of the inventive yeasts are as described below.
1. The yeasts have a leavening ability of dough blended with sugar in an amount of 5 to 25% to flour for bread loaf and confectionery bread (in the low to high sugar range), at the same level as that of routine general types of yeast (for example, Regular Yeast manufactured by Oriental Yeast Co., Ltd), by the straight dough method and the sponge dough method, to produce bread of large volume and stable quality.
2. The yeasts have sugar tolerance (osmotic pressure tolerance) capable of fermenting dough at a very high sugar concentration, such as dough containing sugar in an amount of 30 to 50% to flour.
Of course, the present yeasts may be used to make variants breads and sweet rolls by using dough containing other sugar in place of sucrose; examples of said other sugar are glucose, fructose, liquid inverted sugar, etc.
Various methods can be adopted so as to obtain the inventive yeasts. By the mating method, for example, the intended strain can be obtained highly efficiently. Firstly, therefore, strains with high fermentative abilities and with a character of increased sugar tolerance are selected from among bakers"" yeast strains. The individual yeast strains are inoculated on a spore forming culture medium in a conventional manner to form the spores; after the examination of the properties of the resulting spores, then, strains with the same bakery performance as general practical yeasts for bread making and also with a high leavening ability of 40%-sugar blended dough are satisfactorily screened from among strains grown by the traditional mating method. It is needless to say that the intended strains may be created by a mutation process. As the mutation process, routine methods can be adopted widely, including physical processes with xcex3 ray, ultraviolet ray and temperature difference, etc. and processes with mutagens such as ethidium bromide, nitrogen mustard, diepoxybiitane, colchicine, peroxide, and purine derivatives.
One of the new yeast strains thus obtained was designated Saccharomyces cerevisiae P-712 and deposited under FERM BP-7034 at National Institute of Bioscience and Humanxe2x80x94Technology Agency of Industrial Science and Technology. The bacteriological properties are described below.
Bacteriological Properties of the Strain P-712
1. Growth state
Good growth in YM liquid culture medium.
Cell morphology: spherical to egg shape; 3 to 7xc3x974 to 8 xcexc.
MM agar culture medium: good growth; colony (white, glossy, and smooth).
2. Ascospore
Formed in potassium acetate culture medium; ascospore of spherical shape.
3. Individual physiological properties
3-1. Optimum growth conditions: temperature of 28 to 32xc2x0 C.; pH 4.5 to 6.5.
3-2. Growth range: temperature of 5 to 40xc2x0 C.; pH 2.5 to 8.0.
3-3. Assimilation of nitrate salt: none.
3-4. Fat decomposition: none.
3-5. Carotenoid generation: none.
3-6. Prominent organic acid generation: none.
3-7. Vitamin requirement: biotin and pantothenic acid.
3-8. Sugar tolerance: sufficient leavening ability can be exerted in dough blended with sucrose above 30 to 40 parts by weight or more to 100 parts by weight of flour.
4. Fermentability and assimilability of carbon source
In accordance with the present invention, furthermore, new yeast strains are provided, having a high leavening ability in a super-high range as well as freezing tolerance.
Various methods can be adopted so as to obtain the inventive yeasts. By the mating method, for example, the intended strain can be obtained highly efficiently. Firstly, therefore, strains with high fermentative abilities and with a character raising both freezing tolerance and sugar tolerance are selected from among bakers"" yeast strains. The individual yeast strains are inoculated on a spore forming culture medium in a conventional manner to form the spores; after the examination of the properties of the resulting spores, then, strains with the same bakery performance as general practical yeasts for bread making and also with a high leavening ability of 40%-sugar blended dough and freezing tolerance are satisfactorily screened from among strains grown by the traditional mating method. It is needless to say that the intended strains may be created by a mutation process. As the mutation process, routine methods can be adopted widely, including physical processes with xcex3 ray, ultraviolet ray and temperature difference, etc. and processes with mutagens such as ethldium bromide, nitrogen mustard, diepoxybutane, colchicine, peroxide, and purine derivatives.
One of the new yeast strains was designated Saccharomyces cerevisiae P-731 and deposited under FERM BP-7035 at National Institute of Bioscience and Human-Technology Agency of Industrial Science and Technology. The bacteriological properties are described below.
Bacteriological Properties of the Strain P-731
1. Growth state
Good growth in YM liquid culture medium.
Cell morphology: spherical to egg shape; 3 to 7xc3x974 to 8 xcexc.
MM agar culture medium: good growth; colony (white, glossy, and smooth).
2. Ascospore
Formed in potassium acetate culture medium; ascospore of spherical shape.
3. Individual physiological properties
3-1. Optimum growth conditions: temperature of 28 to 32xc2x0 C.; pH 4.5 to 6.5.
3-2. Growth range: temperature of 5 to 40xc2x0 C.; pH 2.5 to 8.0.
3-3. Assimilation of nitrate salt: none.
3-4. Fat decomposition: none.
3-5. Carotenoid generation: none.
3-6. Prominent organic acid generation: none.
3-7. Vitamin requirement: biotin and pantothenic acid.
3-8. Freezing tolerance/sugar tolerance: after thawing of the frozen dough containing 40 parts by weight of sucrose per 100 parts by weight of flour (under 4-week storage), the strain generates CO2 100 ml or more per 40 g of the dough containing 0.4 g yeast on a dry weight basis at 30xc2x0 C. for 2 hours.
4. Fermentability and assimilability of carbon source
The above-mentioned two yeast strains deposited are considered to belong to Saccharomyces cerevisiae; the strains have the bacteriological properties described above, but the strains have high fermentation potencies in the super-high sugar range and also in the low to medium sugar range. Such strains have never been found among conventionally known yeast strains. Hence, the two yeast strains are designated new strains. Furthermore, not only the above two new strains are encompassed within the scope of the invention; but also all yeast strains having the properties described above, including artificially created strains and strains from the natural origin, are encompassed within the scope of the invention.
(1) The inventive yeast strains with high leavening abilities in the super-high sugar range may be selected and grown in the manner described below. Those with high sugar tolerance can be obtained, by separating each yeast strain generating CO2in the amount of 110 ml or more at 30xc2x0 C. for 2 hours, per 40 g of dough containing 0.4 g of said each yeast strain on a dry weight basis containing sucrose of 40 parts by weight per 100 parts by weight of flour. The inventive strains are sometimes referred to as xe2x80x9cUS yeastxe2x80x9d.
(2) The inventive yeast strains with a high leavening ability in the super-high sugar range and freezing tolerance may be selected and grown in the manner described below. After the thawing of frozen dough containing 40 parts by weight of sucrose to 100 parts by weight of flour, each yeast strain generating CO2 in the amount of 100 ml or more at 30xc2x0 C. for 2 hours per 40 g of the frozen dough containing 0.4 g of said each yeast strain on a dry weight basis is satisfactorily separated. The inventive strains are hereinafter sometimes referred to as xe2x80x9cFD-2 yeastxe2x80x9d.
In accordance with the invention, occasionally, the aforementioned two yeast strains (1) and (2) are collectively called sugar super-tolerant yeast strain.
Owing to the excellent sugar tolerance capable of overthrowing the state of art, the sugar super-tolerant yeast can be used widely for the production of bread items with no sugar to bread items in a low sugar range, like French bread and white bread, as well as confectionery bread and fermented confectioneries prepared from dough at super-high sugar contents, as well as for the production of various bread items using fat or fatty oil or egg or the like. The sugar super-tolerant yeast can be used, for example, for producing coffee cake (bread suitable with coffee, which is preferred by many Americans), bean-jam sweet roll, fruit bread, pastry, butter rolls and croissants.
The process of producing bread using the yeast of the yeast of the present invention is satisfactorily any scratch process (straight dough method and sponge dough method) in a conventional manner and is applicable to frozen bread dough in addition to general bread dough. Examples of the invention are described below.